The invention relates to a latch needle, in particular for knitting machines, with the features as listed in the preamble to patent claim 1.
Latch needles are used for different types of knitting machines in use. A latch needle is known, for example, from German Patent 1113537. The latch needle has a needle body with a hook formed onto its end. A latch slot is formed near the hook, in which a latch is positioned so as to pivot. The latch slot cheeks and the side surfaces of the latch shank function to guide the latch on the side. As a result, the latch can rest with its free end, the so-called latch spoon, on the hook tip and can thus close off the trapping clearance. From this closed position, the latch can pivot back to the latch upright position, in which it frees the trapping clearance. A rivet or pin ensures the pivoting positioning of the latch.
The pivoting movement should be as easy as possible. Modern knitting machines often require needles with extremely easy-moving latches, which should also be guided with the highest possible precision. The easy movement should be ensured for new needles as well as old ones. Needles with hard-to-move latches knit irregularly and thus create a poor loop picture.
The latches of some machines must return during the knitting operation to the upright position as a result of their own weight. If this does not happen reliably, the danger exists that the latches come in contact with machine parts, e.g. the yarn-feed apron, and are thus bent.
The easy movement of the latch can be achieved with increased latch play. Dirt, fiber residues and the like, which enter the latch slot, can consequently cause fewer problems for the smooth running of the latch. The increased latch play, however, worsens the latch guidance even if the needle is still new because the needle latch spoon can no longer hit the hook precisely and thus cannot reliably close off the yarn trapping clearance. With increasing wear, the latch guidance becomes more and more difficult, which in turn can reduce the operational reliability.
A different problem is caused by the increased latch play if the latch is positioned with rivets punched out of the slot cheeks, as disclosed in U.S. Pat. No. 1,991,140. The latch that is provided with a pivoting opening is inserted into the latch slot to position the latch. Following this, portions of the slot cheeks are subsequently pressed or punched toward the inside with the aid of two pressure feet (plunging tools), such that these enter the pivoting opening for the latch and form a positioning rivet for the latch. This operation requires relatively little latch play. In particular with the area surrounding the pivoting opening, the latch forms an abutment for the pressure or punching operation. If the latch is noticeably smaller than the latch slot, a precise positioning of the latch for the punching or pressing operation is not possible. As a result, the latch needle possibly cannot be produced with the desired quality.
During the latch closing movement, the thread or a yarn glides along the surface of the latch slot cheeks, driven by the underside of the latch shank, and into the hook clearance. In the process, the problem of the thread being damaged by sharp edges of the latch slot or the latch shank occurs with increasing frequency and, in the extreme case, can lead to a break in the thread.
Another problem that can occur with increased play between latch shank and latch slot is that the thread is caught between the latch shank and the cheek of the latch slot. This reduces the easy mobility of the latch and can even lead to the needle becoming totally inoperable.
Starting with this, it is the object of the invention to provide a latch needle with a precisely guided, easy moving latch.
The above object generally is achieved by a latch needle having the features according to the present invention.
The latch needle according to the invention is provided with a latch slot that is delimited by two cheeks, the insides of which are positioned opposite each other. The inside surfaces of the cheeks are respectively divided into at least two surface regions, one of which is located directly adjacent to the pivoting mechanism and thus forms a pivoting surface. This surface area advantageously surrounds the pivoting mechanism and functions to guide the latch on the side, thus limiting its pivoting play on the side. The other surface area is positioned at a distance to the pivoting mechanism and defines a comparably larger slot width. The cheek is recessed, so-to-speak, in this surface area so that a clearance develops between the latch shank and the latch slot cheek, which promotes the easy movement of the latch. The clearance that develops between the latch shank and the cheek can take up fiber filaments without this essentially reducing the easy movement of the latch. Threads, fibers or filaments and dust in particular can thus be prevented from being caught between the cheek and the latch shank.
The latch needle according to the invention combines improved latch guidance with decreased frictional resistance and additional clearance space for fibers and filaments.
This applies in particular if the measure according to the invention is not used on one cheek only, but on both cheeks. The resulting latch needle is symmetrical relative to a center plane on which the pivoting axis of the latch is positioned perpendicular. With this latch needle, the frictional resistance of the latch is reduced on both sides.
For the needle according to the invention, the latch slot width is narrower in at least one location near the pivoting mechanism than in at least one other location, at a longer distance thereto. An edge, a step or a curved section can be used as transition between the corresponding surface areas on the cheek inside. The edge between the two surface areas can be either sharp or round. The surface areas can have a flat or arched design. In particular, the surface area that is arranged at a distance to the pivoting mechanism can be curved.
Whereas the cheek surface areas, which define a narrow slot width, are formed at the pivoting mechanism or around it, the other surface areas are preferably located at the area where the slot ends and follow the needle outline, for example the needle top surface. The surface areas in that case can form a strip that adjoins the area where the slot ends. Alternatively, the respective cheek surface area can be recessed and shaped in such a way that a projection is formed on both sides of the latch shank at the respective cheek, which serves the same purpose as a washer arranged on the rivet. These projections center and guide the latch in the center of the latch slot.
The pivoting mechanism for the latch needle preferably is a continuous rivet, but can also be a divided one. The latter can be produced in that portions of the cheek are pushed into a latch opening during a reshaping process. The rivet can be produced by punching it out of the cheek or by inserting a separate pin.
The tongue play on the side advantageously amounts to only a few 1000th millimeters, e.g. approximately 0.02 millimeters or less, near the pivoting mechanism. In contrast, the latch play in the expanded latch slot region (other surface areas) is noticeably higher, for example more than 0.03 millimeters. A sufficiently large slot or clearance space is thus created between the side surfaces of the latch and the cheek insides. This gap or clearance can be uniformly wide or can be shaped in the form of a wedge and preferably extends over at least a portion of the latch pivoting range. The gap or clearance can be divided into sections that can extend, for example, from the pivoting end positions to near the area of the pivot. To facilitate the complete return of the latch to the upright position, the expanded latch slot region can also extend further to the location where the latch is standing upright.
Additional advantageous details of the invention follow from the subsequent description, the drawing or the dependent claims.